Bitumen is used as paving, roofing, joint compound and adhesives. Bitumen is an inexpensive material for these uses, but has many shortcomings, including low flexibility, low tensile strength and poor resistance to degradation due to exposure to oxygen, sunlight and water. Some of these deficiencies in physical properties may be at least partially overcome by including in the bitumen composition various elastomeric polymers and reinforcing fillers such as carbon black. But the usefulness of these bitumen-polymer compositions is seriously limited by the tendency of elastomeric polymers to be incompatible with the bitumens and to separate into a polymer rich phase and an asphaltene rich phase upon storage.
Raley (U.S. Pat. No. 3,669,918) discloses a blend of bitumen and a random copolymer of propylene and ethylene. The composition is said to have good low temperature elasticity and good high temperature impact strength. The process disclosed to blend the polymer and the bitumen consists of placing the polymer in a hot-roll mill and adding bituminous material portion-wise until the desired proportion of bitumen has been added. Alternatively, the copolymer is fluxed into a portion of the molten asphalt, and when a homogenous mixture is obtained, the balance of the asphalt is added. Raley does not disclose a method to combine bitumen carbon black and elastomeric polymers.
Holden (U.S. Pat. No. 3,265,765) provides elastomeric block copolymers A-B-A which may be dispersed in bitumen to improve high temperature viscosity and low temperature ductility and flexibility. The elastomers may be mixed with usual rubber compounding materials such as carbon black. The A blocks of Holden's copolymer are blocks of polymerized alkenyl aromatic hydrocarbons, and the B block is a block of polymerized conjugated diene. A method to prepare such a composition wherein the composition has good storage stability is not disclosed by Holden.
Nielsen (G.B. Specification No. 1,143,895) discloses compositions of bitumen, fillers, carbon black and block copolymers. The block copolymer has an A-B-A configuration where the A blocks are polymerized vinyl-substituted aromatic hydrocarbons, and the B block is an elastomeric block of an alkene, a conjugated diene or a hydrogenated derivative thereof. Nielsen also discloses a process for preparing the composition wherein the carbon black is premixed into a portion of the bitumen, producing a master batch. The copolymer may then be added to the master batch. Alternatively, the copolymer may be blended into the remaining bitumen to form a second master batch and then the two master batches combined. Although the properties of the composition disclosed by Nielsen are excellent, a relatively large amount of block copolymer is required to obtain these properties. The copolymer is considerably more expensive than the other components of the composition, so it would be advantageous to gain the improvements in the bitumen properties achieved by the addition of block copolymers with less copolymer necessary. Applicants have also found that the compatibility of the compositions prepared by the process of Nielsen, as measured by the amount of phase separation during hot storage of the composition, is also deficient.
Van Beem et al. (U.S. Pat. No. 3,978,014) discloses a bituminous composition which is said to have excellent storage stability. Van Beem's bituminous composition comprises: 95-75% by weight of a bituminous component having an aromaticity exceeding 0.004 X P+0.280, where P is the n-heptane asphaltene content; 4-15% by weight of a block copolymer which is preferably a polystyrene-polyakadiene-polystyrene block copolymer and 4-15% by weight of a thermoplastic polymer, different from the block copolymer, which has a molecular weight above 10,000, a solubility parameter of 7.8 to 8.8, and a crystallinity below 60% at 25.degree. C. Van Beem does not disclose a process for combining carbon black in the disclosed bitumen-block copolymer mixture.
It is therefore an objective of the present invention to provide a process for preparing compositions of bitumen, carbon black and block copolymers, the block copolymers containing two or more blocks of a polymerized vinyl substituted aromatic hydrocarbons, and one or more blocks of polymerized conjugated dienes, or hydrogenated derivatives thereof wherein the product of the process has excellent storage stability, tensile properties and weatherability. In another aspect, it is an objective of this invention to provide a bitumen-polymer-carbon black composition which is the product of this process. In another aspect, it is an objective of this invention to provide a bitumen-polymer-carbon black composition which does not phase separate upon high temperature storage. In a preferred embodiment, it is an objective of this invention to provide a roofing composition.